Bulletin No.
AN 116
Page 1 of 2
Da te Is s ue d
August 1999
Index Keys
Corrosion Rate Calculations Weight Loss Coupons
Application Note Corrosion Rate Calculations from Coupons
To calculate corrosion rate from weight loss coupons, use the following equation: CORRO CORROSI SION ON RATE (mpy (mpy))
=
22,30 22,300 0
×
Weig Weight ht Loss Loss (grams (grams))
2 Me Metal Densit sity (g / cm3 )× Coupo upon Area rea (in. (in. )×
Time (days days))
where “Weight Loss” is the weight loss due to corrosion and is determined by subtracting the weight after cleaning from the initial weight, “Metal Density” is the density of the coupon or coupon alloy from the following table, “Coupon Area” is the surface area of the coupon that is exposed to the corroding process, and “Time” is the period in days between installation and removal of the coupon. The above equation is used for calculation of corrosion rates in mpy (mils per year) when the area of the coupon is in inches and the time of exposure is in days. For other units of measure of these parameters, parameters, alternate values for the constant should be substituted for the value 22,300 in the above equation. The following list contains some alternate values. Units of Measure Corrosion Rate (mm/year), Coupon Area (in. 2) Corrosion Rate (mpy), Coupon Area (cm. 2) Corrosion Rate (mm/year), Coupon Area (cm. 2)
Substitute for Value of 22,300 566 143,700 3,650
EXAMPLE A mild steel coupon weighing 10.9265 grams and having an exposed area of 2.96 square inches was installed in a process on August 27 th. On November 13th, after 78 days in the process, it was removed and cleaned. The weight was found to be 10.5560 10.5560 grams. From the following table, table, the density is found to be 7.85 7.85 g/cm 3. The corrosion rate calculation for the period is: 22,3 22,300 00 × (10. (10.92 9265 65 − 10.5 10.556 560) 0) 7.85
×
2.96
×
78 days
=
4.56 mpy
STANDARD COUPON AREAS 3" Strip COSASCO® High Pressure Coupon
5.2 in.2
COSASCO® Multi Disc Coupon
2.3 in.2
6" Strip COSASCO® High Pressure Coupon
11.4 in.2
3" Strip COSASCO® Scale Coupon
5.25 in.2
2" COSASCO® Ladder Coupon
3.4 in.2
3" Stri Strip p Mod Model el 6210 6210 Coup Coupon on (Ret (Retra ract ctab able le))
3.4 3.4 in. in.2
COSASCO® Flush Disc Coupon
2.5 in.2
3" Strip WTC Coupon
3.4 in.2
Corrosion Rate Calculations from Coupons
AN 116
Page 2 of 2
UNS Code
Density (g/cm3 )
CORRATER® Multiplier
Aluminum, 1100
A91100
2.71
0.94
Aluminum, 2024
A92024
2.78
0.86
Brass, Arsenical Admiralty
C44300
8.52
1.67
Brass, Aluminum Arsenical
C68700
8.33
1.62
Brass, Phosphorized Admiralty
C44500
8.52
1.68
Carbon Steel, Pipe Grade
K03005
7.85
1.00
Carbon Steel, 1010
G10100
7.86
1.00
Carbon Steel, 1018
G10180
7.86
1.00
Carpenter 20-Cb3
N08020
8.08
0.98
Cast Iron, Gray
F12801
7.19
1.00
Copper
C11000
8.91
2.00
Copper-Nickel, 90/10
C70610
8.94
1.80
Copper-Nickel, 70/30
C71500
8.94
1.50
Inconel 600
N06600
8.51
0.95
Incoloy 800
N08800
7.94
0.89
Incoloy 825
N08825
8.14
0.88
Lead
L50045
11.34
2.57
Monel 400
N04400
8.84
1.13
Monel K-500
N05500
8.47
1.04
Nickel 200
N02200
8.89
0.93
Stainless Steel, 304
S30400
8.02
0.89
Stainless Steel, 304L
S30403
8.02
0.89
Stainless Steel, 316
S31600
8.02
0.90
Stainless Steel, 316L
S31603
8.02
0.90
Stainless Steel, 2205 Duplex
S31803
7.80
0.89
Titanium, Gr. 2 & 4
R50400
4.54
0.75
Zinc
Z17001
7.13
1.29
Alloy
